1. Field of the Invention
The present invention generally relates to an information transmission system for use in an automated home information system and more specifically to a gateway being provided in the information transmission system, which uses a leased line (employing, for example, a coaxial cable) and a power line as information transmission lines and exchanges information therebetween, and being used to exchange a signal between the leased and power lines.
2. Description of the Prior Art
FIG. 1 is a block diagram showing a prior art load control system for use in a house disclosed in Japanese Patent Public Disclosure No. 149242/85 Official Gazette. As shown in this figure, this load control system is provided with a leased and power lines. Reference numerals 1 indicates a dwelling house which being rebuilt or to which being made an extention. Further, reference numerals 2 and 3 indicate: a coaxial cable used as a leased line; and a power line, respectively. Furthermore, reference numeral 4 designates an additional room A which is provided with a leased-line transmission system a including: the coaxial cable 2; and a controller 5 for controlling other parts of the system a. This transmission system a controls loads 6 such as a door phone and lighting fixtures. On the other hand, reference numerals 7 and 8 indicate initially-established-rooms B and C in which loads 10, namely, lighting fixtures and plug sockets and so forth are controlled by a power-line transmission system b using a power line 3 and being provided with a controller 9 for controlling other portions of the transmission system b.
Reference numeral 11 indicates a gateway intervening between the coaxial cable 2 and the power line 3. This gateway 11 receives control signals from one of the two systems a and b and converts the format of the control signals into another format required by the other system and transmits the converted signals to the latter system when these control signals are exchanged by the two systems a and b. This permits the controller 5 to remotely control the loads 10 such as the lighting fixtures connected to the power line 3. Further, reference numeral 12 indicates a branching portion.
FIG. 2 shows the conventional manner of connecting the gateway 11 to directional couplers 13 and 14 as described in the above cited Japanese Patent Public Disclosure Official Gazette. As shown in this figure, the gateway 11 is connected to both the coaxial cable 2 and the power line 3 by way of the directional couplers 13 and 14. FIG. 3 is a block diagram showing the inner construction of the prior art gateway 11. In this figure, reference numerals 15 and 16 indicate signal detecting and receiving circuits respective which detect and receive signals from the coaxial cable 2 and those from the power line 3. Further, reference numerals 17 and 18 indicate data converting circuits which convert the format of the signals received by the circuits 15 and 16 to another format applicable to the coaxial cable 2 and the power line 3, respectively. Reference numerals 19 and 20 designate data signal transmitting circuits which are used to transmit the converted signals to the coaxial cable 2 and the power line 3, respectively. That is, this gateway 11 detects only data signals in the signal detecting and receiving circuit 15 and then convert, in the data signal converting circuit 17, the received data signal into another data signal having format applicable to the transmission on the power line 3. Furthermore, the gateway 11 sends out the converted data signal to the power line 3 through the data transmitting circuit 19. Similarly, the gate way 11 converts the data signal received from the power line 3 in the signal detecting and receiving circuit 16 and also converts the data signal into another data signal having format applicable to the transmission through the leased line in the data signal converting circuit 18 and further issues the converted signal to the leased line or coaxial cable 2.
An operation of the above described conventional gateway in case of remotely controlling loads 10 by the controller 5 of the leased-line transmission system will be explained hereinbelow by way of example.
First, the controller 5 issues a "load-on" control request signal to the coaxial cable 2. In the gateway 11, the signal detecting and receiving signal 15 receives this signal and the data signal converting circuit 17 converts this signal into a signal having another format applicable to the power line transmission system b. Further, the data signal transmitting circuit 19 sends out the converted signal to the power line 3. Next, a response signal from the load 10 indicating that the load 10 has been into an "on-state" is issued to the power line 3, that is, to the controller. This response signal is received at the signal detecting and receiving circuit 16 of the gateway 11 and is converted in the data signal converting circuit 18 into a signal having another format applicable to the leased-line transmission system a. Further, the data signal transmitting circuit 20 transmits this converted signal to the coaxial cable 2.
The above-mentioned conventional system for exchanging signals between the coaxial cable 2 and the power line 3 through the gateway 11 permits any user in each room of the dwelling house 1 to remotely control the loads such as the lighting fixtures.
The prior art gateway is constructed as above stated. Thus, a transmission of a signal from the coaxial cable 2 to the power line 3 and another transmission of a signal effected in the opposite direction are independent each other because these transmissions are effected by using two independent circuit systems as above-mentioned. Therefore, when a communication between the transmission systems a and b fails, it is impossible to localize a defective portion of the prior art gateway. This degrades reliability of the prior art gateway considerably.
Further, as described above, the prior art gateway provides functions of transmitting and receiving signals and performs only transitions of signals between the leased and power lines but does not control the transmission systems. Therefore, in case of performing a centralized control of the power line transmission system, the load control system needs further providing a controller for controlling the power-line transmission system. This results in that the load control system becomes much expensive, that much complicated communications are necessary to control the system and that an efficiency in signal processing is considerably reduced.
Furthermore, the prior art gateway constructed as above described has encountered a serious problem that efficiency in exchanging signals between the leased and power lines is low. This low efficiency is owing to a large difference in transmission rate between the leased and power lines. The leased line or coaxial cable can transmit signals at a high rate such as 9600 bps, while the power line ought to transmit signals at a low rate such as 100 bps in order to ameliorate its reliability because the power line has a relatively large noise in comparison with the leased line. For instance, the prior art gateway converts the control request signal received from the leased line and transmits the converted signal to a load through the power line having such a low transmission rate even when the load is not currently being used and disconnected to the power line. Consequently, there ought to occur many extra retransmissions of signals and very long wait for a response in the prior art system.
Moreover, the conventional information communication system constructed as above described has a defect that when signals received from the coaxial cable are uniformly converted and then transmitted to the power line, an overload is to be carried through the power line and the response from the load is harmed. This is partly because that as above-mentioned, there is a large difference in transmission rate between the leased and power lines and partly because that the information is not always transmitted in a way reasonable enough for the purpose of increasing the efficiency in the transmission.
Hereinafter, the latter reason will be more detailedly explained. First, the information to be transmitted in the automated home system is roughly classified into the following two kinds of the information:
(i) control information to be used to control domestic operations in the automated home system; and
(ii) text to be used in, for example, a personal computer in the automated home system.
As to the control information, it does not matter how to represent or code the information as long as the load, for example, the light can be controlled by a certain control command and turned on. Contrarily, in case of the transmission of a text, a representation or code used to represent the information or text is very important. This is because all characters of the text are on an equal footing in constituting the information or text to be transmitted.
Therefore, in case of a transmission of data signals from the coaxial cable to the power line by way of the gateway, it is reasonable and preferable that the gateway can operate as follows:
(1) First, the gateway discriminates the control information from the text.
(2) Subsequently, the gateway compresses the discriminated control information before transmitting it to the power line. In that event, the control information is to be compressed to the extent sufficient to cause the power line transmission system to operate as it directs. On the other hand, with refrence to the data identified as a text, the gateway transmits it to the power line without compressing it.
The present invention is accomplished to solve the above described problems in the prior art.